The field of the invention relates in first instance to an injection combustion engine with electric spark ignition comprising at least one cylinder having an air inlet duct, at least one inlet valve disposed in a cylinder head, at least one fuel injector, and a heating element with a heat sink disposed downstream of the injector having one or more PTC tablets thereon.
A combustion engine of this type is know from German Patent DE-C-3,426,469 and Dutch Patent NL-A-8,801,334.
It appears that about 50% of the total exhaust gas pollution emission from operation of an engine is formed in the brief period before the engine reaches its operating temperature. Even exhaust gas catalysts, which under normal conditions reduce the exhaust gas pollution emission by about 90%, achieve this degree of conversion only when the operating temperature of the catalyst is reached. The conversion begins at a temperature of about 300.degree. C. so that at first after a cold start the exhaust gas pollution emission of the engine with a catalyst is reduced little or not at all. Since the temperature level is not high enough to fully vaporize the fuel (gasoline or alcohol) in a cold engine, an extra amount of fuel has to be added to the cold engine in order to obtain a combustible mixture. This leads to a high exhaust gas pollution emission. At low engine temperatures, therefore, both fuel consumption and exhaust gas pollution emission tend to be relatively high. The heating of the fuel/air mixture by the heating element therefore makes a substantial contribution to improving environmental quality and at the same time leads to a substantial saving in fuel, inasmuch as little or no extra fuel needs to be injected. In the combustion engine described above, the fuel is sprayed onto a heating element which has been quickly brought to the desired temperature and the fuel is thus brought to the desired temperature. The fuel will vaporize better and at the same time a better mixture with the combustion air will be obtained. The heating element is disconnected when the engine is hot enough to take over the vaporization of the fuel.
In the engine known from the said German Patent DE-C-3,426,649, the heating element is made in the form of a pipe projecting into the inlet duct of the cylinder and surrounded by an insulating tube. The pipe and the tube have a border flange fitting in a recess in the cylinder head and fixed by the air inlet duct. One drawback of this design is that installation and replacement of the heating element is a time-consuming chore. A similar drawback is found in the engine according to Dutch Patent NL-A-8,801,334 where the heating element is integrated in a plate clamped between the inlet duct and the heat of the cylinder.